Financial Markets
Financial markets connect agents who need financing (firms, States) with those who have savings to invest. Together with financial intermediaries (banks, funds), they form what Mankiw calls the financial system, ensuring the efficient allocation of capital and the pricing of risk through the mechanisms of supply and demand.
Last updated: 9 July 2026
Definition
DefinitionA financial market is a venue (physical or electronic) where financial instruments are traded: stocks, bonds, currencies, derivatives, and commodities. A distinction is drawn between the primary market, where securities are issued for the first time (initial public offering, bond issuance), and the secondary market, where already-issued securities are exchanged between investors (the day-to-day stock exchange).
The two main segments are the stock market, where ownership shares of firms are traded, and the bond market (debt market), where debt securities issued by States or firms are traded. The money market concerns short-term debt securities (less than one year), while the capital market covers longer maturities.
Why it matters
Financial markets fulfill essential macroeconomic functions: they channel savings into productive investment, set the price of risk, enable the management and transfer of risk between agents, and transmit economic information in real time through asset prices.
The 2008 financial crisis demonstrated that a malfunction of financial markets can trigger a global economic crisis.
Key points
The fundamental relationship between return and risk: in the long run, riskier assets (stocks) offer higher returns than less risky assets (bonds), which themselves outperform risk-free assets (regulated savings). Mankiw cites historical data showing that U.S. stocks have returned on average ~7% per year in real terms over a century. Real return ≈ nominal return − inflation
The efficient market hypothesis implies that an investor cannot systematically obtain returns above the market without taking more risk. Low-cost index funds are therefore a rational strategy for most savers
Diversification is the only way to reduce risk without reducing expected return. Mankiw illustrates this principle by showing that a portfolio of 20 well-diversified stocks carries markedly less risk than a single stock
Financial markets are not always efficient: speculative bubbles (dot-com in 2000, real estate in 2007) and crashes show that prices can deviate durably from fundamentals
Concrete example
ExamplesThe CAC 40 groups the 40 largest listed French firms (LVMH, TotalEnergies, L'Oréal, Sanofi, etc.). Its value reflects investors' expectations about the future performance of these firms and, by extension, of the French economy. The S&P 500, the benchmark index in the United States, has risen on average about 10% per year (including dividends) over the last 50 years. In 2024, global market capitalization was around $128 trillion, dominated by the U.S. market (more than 50% of the total, sharply higher thanks to the concentration in technology mega-caps).
Mankiw anecdote
MankiwMankiw recalls that over the very long run, stocks have outperformed bonds and money-market placements across the major economies studied (a consensus confirmed by the work of Dimson, Marsh and Staunton) — though this is no guarantee: there have been 30-year windows in which bonds came out ahead, such as in the United States between 1981 and 2011. However, in the short run, they are far more volatile: the S&P 500 lost 57% between October 2007 and March 2009 during the financial crisis, before fully recovering its losses in four years. Mankiw concludes that patience and the investment horizon are the most important determinants of investment success.
Market impact
MarketsFinancial markets react in real time to macroeconomic data (GDP, inflation, employment), to central bank decisions (policy rates, QE), to corporate earnings, and to geopolitical events. Correlations between asset classes are not stable: in crisis periods, correlations rise (contagion effect) and diversification offers less protection than in normal times. Understanding how financial markets function is indispensable for interpreting price movements and adapting one's investment strategy to one's time horizon and risk profile.